Refrigerant charging system and method for variable speed compressor based ac system

ABSTRACT

The present disclosure relates to the field of air conditioning technology. In particular, it involves a refrigerant charging method for variable speed compressor based ac system.

BACKGROUND OF TIE DISCLOSURE

The disclosure below will assume common knowledge of air conditioning and heat pump as well as their heat exchange principle in terms of achieving cooling and heating. Therefore, when discussing particular AC inner working, it is applied to heat pump collectively. The discussion will also treat compressor speed and compressor RPS (rotation per second) interchangeably as well.

With the development of air-conditioning technology, variable speed air conditioner is becoming mainstream product because it is energy efficient, low noise and good thermostatic, etc. Conventional variable speed air conditioner generally includes an indoor unit, an outdoor unit, control wires and refrigerant lines between indoor unit and outdoor unit. The control wires and refrigerant lines are usually berried into building structure. It is also not a practical approach to redo control wires and refrigerant lines. Even upgrading them might not be an option in some cases due to the building structure itself. Therefore, when upgrading old AC system to new one, the existing control wires and refrigerant lines are kept.

On the other hand, because length of existing refrigerant lines and the indoor unit size (the inner volume of the coil) are not known during upgrade, technicians cannot charge the system precisely.

When the system is over charged, the evaporator performance is severely affected, and so is the system's cooling efficiency. In worse cases, it could also lead to compressor damage because of the liquid slugging. Conversely, when the system is under charged, the cooling capacity is lowered due to smaller refrigerant rate flow, in effect lowering the system's cooling efficiency. It is apparent that in this field, there needs to be a robust method to precisely charge the refrigerant, even when the length of refrigerant lines and indoor unit volume are not possible to be determined.

SUMMARY OF THE DISCLOSURE

Based on the above deficiencies, an objective of the disclosure is to provide a new system and method for variable speed AC system refrigerant charging implementation, so to precisely charge the refrigerant, even when the length of refrigerant lines and indoor unit parameters are not possible to be determined, in order to guaranteed the AC system runs under an optimal efficiency.

The variable speed AC system comprises at least: a variable speed compressor, a reversing valve, a thermal expansion valve (TXV), a defroster, a condenser, an inlet temperature sensor to compressor, an outlet temperature sensor to compressor, a suction pressure sensor, a discharge pressure sensor, a liquid line temperature sensor, outdoor air temperature sensor, defroster temperature sensor, evaporator and controller.

Before determining the refrigerant charging diagnosis, the AC system should be run for a predetermined time under a predetermined speed, where the speed is chosen based on the AC tonnage.

Subsequently, from to the various sensors of the air conditioning system, the following parameters are obtained: compressor suction pressure LP, compressor discharge pressure HP, evaporating temperature TE corresponding to the compressor suction pressure LP, condensing temperature TC corresponding to compressor discharge pressure HP. The evaporating temperature TE and the condensing temperature TC can be obtained from refrigerant property table by the values of the compressor suction pressure LP and the compressor discharge pressure HP. Also obtained from sensors are liquid line temperature TL, compressor inlet side temperature TS, compressor outlet side temperature TD, defroster temperature TH, and outdoor air temperature TA.

According to the above parameters, the next step is to calculate the liquid line sub-cooling degree SC, the compressor inlet superheat degree SH, the compressor outlet superheat degree DSH, and the outdoor heat exchanger heat transfer temperature difference ΔT.

Subsequently, it is time to determine whether or not the thermal expansion valve (TXV) is at a proper opening degree based on the compressor inlet superheat degree SH and the compressor outlet superheat degree DSH.

When the thermal expansion valve (TXV) opening is at an appropriate level, it is time to determine whether the refrigerant is sufficiently reaching an appropriate level according to value range of the refrigerant coefficient X.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a variable speed AC compressor control system configuration, according to first embodiment of this disclosure.

FIG. 2 shows a system diagram of the control method of variable speed AC system, under cooling operation according to the first embodiment of this disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE First Embodiment

FIG. 1 is the variable speed AC system configuration diagram of the first embodiment. As shown, it comprises: a variable speed compressor 1, a reversing valve 2, a thermal expansion valve (TXV) 3, a defroster 4, a condenser 5, an inlet refrigerant temperature sensor 6, an outlet refrigerant temperature sensor 7, a suction pressure sensor 8, a discharge pressure sensor 9, a liquid line temperature sensor 10, outdoor air temperature sensor 11, defroster temperature sensor 12, evaporator 13 and controller 14.

FIG. 2 shows a system diagram of the control method of the variable speed AC system, under cooling operation according to the first embodiment. Before determining the refrigerant charging diagnosis, the AC system should be run for 15-20 minutes under a predetermined speed, where the speed is chosen based on the AC tonnage chart below:

Tonnage 2 3 4 5 Speed 56 66 56 66 (cooling)/RPS

From the chart, if the system is 4 tons or 5 tons, the compressor discharge volume is about twice as when the system is 2 tons or 3 tons. Therefore, the 4 ton and 5 ton system would run at a speed at 56 RPS and 66 RPS.

Subsequent to running for the predetermined time, from to the various sensors of the air conditioning system, the following parameters are obtained: compressor suction low pressure LP, compressor discharge pressure HP, evaporating temperature TE corresponding to the compressor suction pressure LP, condensing temperature TC corresponding to compressor discharge pressure HP. The evaporating temperature TE and the condensing temperature TC can be obtained from refrigerant property table by the values of the compressor suction pressure LP and the compressor discharge pressure HP. Also obtained from sensors are liquid line temperature TL, compressor inlet side temperature TS, compressor outlet side temperature TD, defroster temperature TH, and outdoor air temperature TA.

According to the above parameters, the next step is to calculate the liquid line sub-cooling degree SC, the compressor inlet superheat degree SH, the compressor outlet superheat degree DSH, and the outdoor heat exchanger heat transfer temperature difference ΔT. The calculations are as follow:

liquid line sub-cooling degree SC=condensation temperature TC—liquid line temperature TL;

compressor inlet gas superheat SH=compressor inlet gas temperature TS−evaporating temperature TE;

compressor outlet superheat DSH=compressor outlet temperature TD−condensing temperature TC;

outdoor heat exchanger heat transfer temperature difference ΔT=condensing temperature TC−outdoor air temperature TA.

Next, it is time to determine whether or not the thermal expansion valve (TXV) is abnormally opened according to the compressor inlet superheat degree SH and the compressor outlet superheat degree DSH. When the compressor inlet gas superheat degree SH<5° F. or the compressor inlet superheat degree DSH<15° F., it is considered that the thermal expansion valve (TXV) opening is too large, which will cause the refrigerant migrated to high pressure side (i.e. condenser coil) goes back to the low pressure side in a large amount. This makes the difficulty of pressure difference establishment between high pressure and low pressure. The refrigerant on the low pressure side of the chamber is not completely evaporated, and the compressor superheat or superheat of the exhaust gas is too low. At this time, it is necessary to adjust the opening of the thermal expansion valve (TXV) to reduce it until the compressor inlet superheat SH≥5° F. or the compressor outlet superheat DSH≥15° F.

Subsequently, the refrigerant coefficient X is calculated, where the refrigerant coefficient X=the liquid line sub-cooling degree SC/the outdoor heat exchanger heat transfer temperature difference ΔT. This value of the refrigerant coefficient is between 0.0 to 1.0. For the first embodiment, the refrigerant coefficient X is set at the numerical value range between Q1 and Q2, considered to be an appropriate level. In this embodiment, Q1 is 0.4 and Q2 is 0.6.

When the refrigerant coefficient X<0.4, it is considered that the refrigerant charge amount is too low, and it is necessary to continue to charge the refrigerant. When the refrigerant coefficient X>0.6, it is considered that the system is overcharged. At this time, in order to avoid the misjudgment of the amount of refrigerant, further determination is needed. As the condensation process of the refrigerant in the outdoor heat exchanger proceeds, the single-phase superheated gas state at the inlet is gradually changed to the gas-liquid two-phase state, and then followed by conversion to single-phase pure liquid refrigerant. Therefore, in the present embodiment, the defrosting temperature TH is used to determine whether or not the amount of refrigerant is excessive. When (condensing temperature TC−defrosting temperature TH)/outdoor heat exchanger heat transfer temperature difference ΔT is greater than or equal to the preset value J, the controller displays the actual X, it is considered that the refrigerant charge amount is too large, and it is necessary to recover a part of the refrigerant. When (condensing temperature TC−defrosting temperature TH)/outdoor heat exchanger heat transfer temperature difference ΔT is less than the preset value J, then the refrigerant charge amount is considered to be suitable at this time, the displayed X in controller is 0.6. The value J is between 0.5 to 0.6 in this embodiment.

Finally, under the premise of ensuring 0.4≤X≤0.6, additional determination can be made for whether the expansion valve opening degree is too small. When the compressor inlet gas superheat degree SH≥25° F. or when the compressor outlet superheat degree DSH≥60° F., it is considered that the thermal expansion valve (TXV) is too small, and the opening of the thermal expansion valve (TXV) needs to be increased. 

1. A variable speed AC charging system comprises: a variable speed compressor, a reversing valve, a thermal expansion valve, a defroster, a condenser, an inlet refrigerant temperature sensor, an outlet refrigerant temperature sensor, a suction pressure sensor, a discharge pressure sensor, a liquid line temperature sensor, outdoor air temperature sensor, defroster temperature sensor, evaporator and controller, wherein the AC system should be run for a predetermined time under a predetermined speed, where the speed is chosen based on AC tonnage; wherein the controller is configured to obtain from to the various sensors of the AC system the following parameters: compressor suction pressure LP, compressor discharge pressure HP, evaporating temperature TE corresponding to the compressor suction pressure LP, condensing temperature TC corresponding to compressor discharge pressure HP; wherein the controller is further configured to calculate compressor inlet gas superheat SH=compressor inlet gas temperature TS−evaporating temperature TE, compressor outlet superheat DSH=compressor outlet temperature TD−condensing temperature TC, and indicate whether the thermal expansion valve (TXV) is opened too much according to the compressor inlet superheat degree SH and the compressor outlet superheat degree DSH; wherein after properly adjusting the TXV opening, the controller is further configured to determine if the AC system is properly charged.
 2. The variable speed AC charging system according to claim 1, wherein the controller is further configured to calculate outdoor heat exchanger heat transfer temperature difference ΔT=condensing temperature TC−outdoor air temperature TA, liquid line sub-cooling degree SC=condensation temperature TC−liquid line temperature TL, and refrigerant coefficient X=the liquid line sub-cooling degree SC/the outdoor heat exchanger heat transfer temperature difference ΔT, and based on the refrigerant coefficient X, determine whether the refrigerant is properly charged.
 3. The variable speed AC charging system according to claim 2, wherein the controller is configured to indicate to reduce the TXV opening when the compressor inlet gas superheat degree SH<5° F. or the compressor inlet superheat degree DSH<15° F.
 4. The variable speed AC charging system according to claim 3, wherein the controller is further configured to display the coefficient X and to indicate the refrigerant is charged correctly when the coefficient X is between Q1 and Q2, where Q1 is 0.4 and Q2 is 0.6.
 5. The variable speed AC charging system according to claim 4, wherein when the coefficient X is greater than Q2, the controller is further configured to calculate J=(condensing temperature TC−defrosting temperature TH)/outdoor heat exchanger heat transfer temperature difference ΔT, and to indicate too much refrigerant when J is greater than or equal to a value between 0.5 to 0.6 or to indicate the refrigerant is charged correctly if J is less than to that value.
 6. The variable speed AC charging system according to claim 5, wherein the controller is further configured to indicate under 0.4≤X≤0.6, whether the TXV opening degree is too small when SH≥25° F. or DSH≥60° F.
 7. A variable speed AC system charging method comprising: running the AC system for a predetermined time under a predetermined speed, where the speed is chosen based on the tonnage; obtaining from to various sensors of the AC system the following parameters: compressor suction pressure LP, compressor discharge pressure HP, evaporating temperature TE corresponding to the compressor suction pressure LP, condensing temperature TC corresponding to compressor discharge pressure HP; calculating compressor inlet gas superheat SH=compressor inlet gas temperature TS−evaporating temperature TE, compressor outlet superheat DSH=compressor outlet temperature TD−condensing temperature TC; indicating whether thermal expansion valve (TXV) is opened too much according to the compressor inlet superheat degree SH and the compressor outlet superheat degree DSH; and after properly adjusting the TXV opening, determining if the AC system is properly charged.
 8. The variable speed AC system charging method according to claim 7, further comprising: calculating outdoor heat exchanger heat transfer temperature difference ΔT=condensing temperature TC−outdoor air temperature TA, liquid line sub-cooling degree SC=condensation temperature TC−liquid line temperature TL, and refrigerant coefficient X=the liquid line sub-cooling degree SC/the outdoor heat exchanger heat transfer temperature difference ΔT; and based on the refrigerant coefficient X, determining whether the refrigerant is properly charged.
 9. The variable speed AC system charging method according to claim 8, further comprising: indicating to reduce the TXV opening when the compressor inlet gas superheat degree SH<5° F. or the compressor inlet superheat degree DSH<15° F.
 10. The variable speed AC system charging method according to claim 9, further comprising: indicating the refrigerant is charged correctly when the coefficient X is between Q1 and Q2, where Q1 is 0.4 and Q2 is 0.6.
 11. The variable speed AC system charging method according to claim 10, further comprising: when the coefficient X is greater than Q2, calculating J=(condensing temperature TC−defrosting temperature TH)/outdoor heat exchanger heat transfer temperature difference ΔT; and indicating too much refrigerant when J is greater than or equal to a value between 0.5 to 0.6 or indicating the refrigerant is charged correctly if J is less than that value.
 12. The variable speed AC system charging method according to claim 11, further comprising: indicating under whether the TXV opening degree is too small when SH≥25° F. or DSH≥60° F.
 13. A non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing a first device to perform steps comprising: running variable speed AC system for a predetermined time under a predetermined speed, where the speed is chosen based on the tonnage; obtaining from to various sensors of the AC system the following parameters: compressor suction pressure LP, compressor discharge pressure HP, evaporating temperature TE corresponding to the compressor suction pressure LP, condensing temperature TC corresponding to compressor discharge pressure HP; calculating compressor inlet gas superheat SH=compressor inlet gas temperature TS−evaporating temperature TE, compressor outlet superheat DSH=compressor outlet temperature TD−condensing temperature TC; indicating whether thermal expansion valve (TXV) is opened too much according to the compressor inlet superheat degree SH and the compressor outlet superheat degree DSH; and after properly adjusting the TXV opening, determining if the AC system is properly charged.
 14. The non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing the first device to perform steps according to claim 13, further comprising: calculating outdoor heat exchanger heat transfer temperature difference ΔT=condensing temperature TC−outdoor air temperature TA, liquid line sub-cooling degree SC=condensing temperature TC−liquid line temperature TL, and refrigerant coefficient X=the liquid line sub-cooling degree SC/the outdoor heat exchanger heat transfer temperature difference ΔT; and based on the refrigerant coefficient X, determining whether the refrigerant is properly charged.
 15. The non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing the first device to perform steps according to claim 14, further comprising: indicating to reduce the TXV opening when the compressor inlet gas superheat degree SH<5° F. or the compressor inlet superheat degree DSH<15° F.
 16. The non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing the first device to perform steps according to claim 15, further comprising: indicating the refrigerant is charged correctly when the coefficient X is between Q1 and Q2, where Q1 is 0.4 and Q2 is 0.6.
 17. The non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing the first device to perform steps according to claim 16, further comprising: when the coefficient X is greater than Q2, calculating J=(condensing temperature TC−defrosting temperature TH)/outdoor heat exchanger heat transfer temperature difference ΔT; and indicating too much refrigerant when J is greater than or equal to a value between 0.5 to 0.6 or indicating the refrigerant is charged correctly if J is less than that value.
 18. The non-transitory computer-readable medium having stored thereon a set of computer-executable instructions for causing the first device to perform steps according to claim 17, further comprising: indicating under 0.4≤X≤0.6, whether the TXV opening degree is too small when SH≥25° F. or DSH≥60° F. 